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Sunday, July 31, 2011

Spy vs Spy

You may recognize that bug right there, performing a little insect arabesque. This is a Japanese beetle (Popillia japonica), a long standing invasive beetle. I remember seeing them in my Aunt's pool as a kid, where they would inevitably seem to get stuck and end up drowning, but not before trying to climb onto you with their pointy little beetle legs. It's been a while since I've seen one, but I suspect it's only because I haven't been looking. While out doing field work I spotted this one, along with a flower crab spider, just barely visible around the bottom of the unopened thistle (slightly better picture of it here, I suspect it got a bit more than it was bargaining for when this beetle showed up). Japanese beetles are notorious for being extremely unpicky eaters: as adults they'll chew up pretty much anything green, and can do serious damage during population peaks.

Interestingly, this one has chosen to settle down for dinner on another invader, the Canada thistle (Cirsium arvense). The Canada thistle is a very, very common invasive weed in this area, particularly along rail road tracks and road sides (this picture is taken less than five meters from the edge of the road). It's very good at crowding out other plants, and is extremely hardy. In this instance, the Japanese beetle (which is not considered a major problem in Indiana) is performing a very slight service by attacking the unopened flower of this plant. In the long run, it wont make much difference that this particular beetle stopped to eat this particular flower. But it does illustrate that invasive management is often not a clear cut thing, as pest species can turn against each other, or perform useful ecosystem services (pdf).

You can read more about controlling Japanese beetles here (pdf), and here.